1. Field of the Invention
The present invention relates to a mechanism capable of moving a platen, which is arranged in close proximity to a head such as a thermal head, so as to separate away from the head, and a thermal printer having the mechanism.
2. Description of the Related Art
Conventionally, in some small thermal printers mounted in, for example, portable information apparatuses, a thermal head and a platen roller are arranged in close proximity to each other, and a sheet material passing through the gap between the two members is heated by the thermal head, thus effecting recording or thermal activation. With this construction, during drive, the platen roller for supporting and conveying the sheet material, and the thermal head that abuts the sheet material to heat the sheet material, are opposed to each other at a small spacing large enough to allow passage of one sheet material therethrough. However, the above construction does not provide a sufficient working space allowing insertion of the operator's hand when, for example, the sheet material jams, when some maintenance is needed on the thermal head or the platen roller, when the sheet material is to be set in position for the first time, etc. In particular, when other various mechanisms, such as a cutter member for cutting the sheet material into an arbitrary length, are arranged in the immediate vicinity of the thermal head and the platen roller to achieve miniaturization, no working space is provided around the thermal head and the platen roller, making it difficult for the operator to directly touch the thermal head and platen roller with his/her hand from any direction during work.
In view of this, JP 2003-200624 A, JP 2002-248820 A, etc. disclose a construction capable of moving the platen roller away from the thermal head. Since a thermal head is often retained inside a casing in order to secure electrical connection for supplying a drive signal, in the construction disclosed, usually a platen roller, which is subject to less constraints than a thermal head, is capable of moving away from a position in close proximity to the thermal head.
In the construction as described in JP 2003-200624 A and JP 2002-248820 A, the platen roller can be removed by releasing a member that holds the platen roller inside the casing of the thermal printer. When the platen roller is thus removed, the front of the thermal head becomes open, thus allowing insertion of the operator's hand to facilitate removal of a jammed sheet material, maintenance on the thermal head, setting of the sheet material in position, etc.
In the construction as described in JP 2003-200624 A and JP 2002-248820 A, the platen roller is removed upward, that is, toward the downstream side in the sheet material passage direction. Accordingly, other components cannot be arranged in close proximity to the thermal head and the platen roller above the thermal head and the platen roller, that is, on the downstream side in the sheet material passage direction. That is, at least, a sufficient space must be secured first to allow the operation of removing the platen roller, and only thereafter, other components can be arranged outside the space. This requirement hinders the overall miniaturization of the apparatus. Further, when, for example, a cutter member for cutting the sheet material into an arbitrary length is to be disposed, the cutter member is located on the downstream side away from the thermal head for effecting recording or thermal activation through the intermediation of a large space secured for the platen roller removing operation, with the result that the sheet material can be cut only at a position spaced at a considerable distance from the heating position, which may result in wastage of the sheet material. To avoid this, a construction may be conceived in which the travelling path of the heated sheet material is changed by bending the same, thus routing the sheet material to a position where it does not obstruct the platen roller removing operation, with a cutter member or the like being disposed so as to cut the sheet material at the position to which it is routed. This construction, however, may lead to an increase in apparatus size or add complexity to the layout of respective components, and further, make smooth conveyance of the sheet material impossible.
The portable apparatus shown in FIG. 7 of JP 2003-200624 A is constructed such that the platen roller can be separated away from the thermal head through rocking motion of the cover member that holds the platen roller, the cover member constituting a part of the casing outer wall. The cover member rocks along a large rocking path. Accordingly, other components cannot be arranged on the downstream side of the thermal head and the platen roller where those components may interfere with the rocking path, making it necessary to adopt a construction in which the heated sheet material is discharged to the outside of the casing as it is. In an alternative conceivable construction, such other components may be arranged on the outer surface of the cover member so that, with the cover member closed, those components exist on the downstream side with respect to the thermal head and the platen roller. However, when the components to be arranged on the outer surface of the cover member are large and heavy, this hinders the rocking motion of the cover member. Further, when a cutter member is to be arranged on the outer surface of the cover member, the cutter member is exposed to the casing exterior, resulting in such disadvantages that the cutter member may cut the operator particularly during the rocking operation, requiring careful handling.